1. Field of the Invention
The present invention relates to a method of generating spin-polarized conduction electrons in a semiconductor device. The present invention also relates to a semiconductor device in which spin-polarized conduction electrons are generated.
2. Related Art Statement
Generation of spin-polarized conduction electrons in a semiconductor material newly applies spin degree of freedom to semiconductor electronic materials, and has been studied towards a future device application. Semiconductor devices generating such spin-polarized conduction electrons are expected to realize a novel application to a spin field effect transistor, a spin-polarized scanning tunneling microscopy, a spin memory device, a circularly polarized light emitting device, etc.
In a conventional technology of generating spin-polarized electrons, spin-polarized electrons are injected into a semiconductor body by using metallic magnetic electrodes. However, in this known method, the spin-polarization generated within the semiconductor body is changed only slightly owing to the Schottky barrier produced at a metal/semiconductor interface.
It is possible to generate spin-polarized electrons by replacing a part of atoms constituting a semiconductor material with magnetic atoms to convert the non-magnetic semiconductor material into a magnetic semiconductor material. However, since the interaction between magnetic spins and electrons is small, the spin polarization is produced only slightly. On the other hand, the interaction between holes in such a magnetic semiconductor and magnetic spins is relatively large and it is possible to give big spin polarization to holes. But a spin relaxation time is very short because of the spin-orbit interaction, and thus the application to the field of electronics is difficult.
Therefore, the purpose of this invention is to provide a method of generating effectively spin-polarized electrons (carriers in the conduction band) within a semiconductor.
It is another object of this invention to provide a semiconductor device, in which spin-polarized conduction electrons can be effectively generated.
According to the invention, a method of generating spin-polarized conduction electrons, characterized in that the method comprises a step for providing a ferromagnetic/non-magnetic heterojunction between a ferromagnetic semiconductor layer and a non-magnetic semiconductor layer having an energy band alignment of Type II with respect to the ferromagnetic semiconductor layer such that a spin splitting of a conduction band of the non-magnetic semiconductor layer is induced by a spontaneous spin splitting of a valence band of the ferromagnetic semiconductor layer to generate spin-polarized conduction electrons in the non-magnetic semiconductor layer.
In the Type II energy band alignment of semiconductor layers, a top of the valence band of one semiconductor layer is located above a bottom of the conduction band of the other semiconductor layer in the energy band diagram. If the ferromagnetic semiconductor layer is connected to the non-magnetic semiconductor layer having the energy band alignment of Type II with respect to the ferromagnetic semiconductor layer, the spontaneous spin splitting of the valence band of the ferromagnetic semiconductor layer induces the spin splitting of the conduction band of the adjacent non-magnetic semiconductor layer and spin-polarized electrons are generated in the non-magnetic semiconductor layer.
According to the invention, a semiconductor device, characterized in that the device comprises a ferromagnetic semiconductor layer, and a non-magnetic semiconductor layer having an energy band alignment of Type II with respect to the ferromagnetic semiconductor, said ferromagnetic semiconductor layer and non-magnetic semiconductor layer being connected to form a ferromagnetic/non-magnetic heterojunction such that a spin splitting of the conduction band of the non-magnetic semiconductor layer is induced by a spontaneous spin splitting of the valence band of the ferromagnetic semiconductor layer to generate spin-polarized conduction electrons in the non-magnetic semiconductor layer.
The method for generating the spin-polarized conduction electrons according to the invention utilizes the fact that the spontaneous spin splitting of the valence band is induced in the magnetic semiconductor, and when the magnetic semiconductor is adjoined to the non-magnetic semiconductor having the energy band alignment of Type II with respect to the magnetic semiconductor layer, the spin splitting of the conduction band of the non-magnetic semiconductor is induced by said spontaneous spin splitting of the valence band of the magnetic semiconductor to generate spin-polarized electrons in the non-magnetic semiconductor.